1. Field of the Invention
This invention relates generally to medical devices and methods of making the same. More particularly the invention relates to balloons for use in medical applications, such as balloons for use with catheters.
2. Discussion of the Related Art
As an alternative to open-heart, coronary bypass surgery, a technique referred to as coronary transluminal angioplasty has been developed. In carrying out this procedure, a dilatation catheter having a balloon on the distal end is routed through the vascular system to a location within a coronary artery containing a stenotic lesion. Following placement of the balloon across the lesion, a fluid is introduced into the proximal end of the catheter and is used to inflate the balloon to a predetermined relatively high pressure whereby the lesion is compressed into the vessel wall restoring patency to the previously occluded vessel.
In conventional stent deploying balloon catheters, the balloon is made of essentially non-compliant material, such as nylon or polyethyleneterephthalate (PET). Such non-compliant material exhibits little expansion in response to increasing levels of inflation pressure. Because the non-compliant material has a limited ability to expand, the uninflated balloon must be made sufficiently large so that, when inflated, the balloon has sufficient working diameter to compress the stenosis and open the patient's passageway. However, a large profile, non-compliant balloon can make the catheter difficult to advance through the patient's narrow vasculature because, in an uninflated condition, such balloons form flat or pancake shaped wings which extend radially outward. Consequently, the wings of an uninflated balloon are typically folded into a low profile configuration for introduction and advancement through the vessel. The wings are again produced upon deflation of the balloon following stent deployment within the patient. These wings on the deflated balloon are undesirable because they result in an increased balloon profile which can complicate withdrawing the catheter after stent deployment.
Although stents have been used effectively for some time, the effectiveness of a stent can be diminished if it is not properly implanted within the vessel. For example, expansion of a balloon folded into a low profile configuration for introduction into the patient, can cause non-uniform expansion of a stent mounted on the balloon.
The non-uniform expansion of conventional designs has resulted in the use of an elastic sleeve around the balloon and under the stent to uniformly distribute force from the expanding folded balloon to the stent. Additionally, such an elastic sleeve can encourage the inflated balloon to deflate into a “wingless”, compact profile.
In many interventional radiology practices, a common indication for balloon angioplasty is for treatment of neointimal hyperplastic stenoses associated with hemodialysis grafts and fistulas. Unlike softer atherosclerotic stenoses, these neointimal hyperplastic lesions can be difficult to dilate and require the use of ultra-high pressure angioplasty balloons, capable of sustaining pressures up to 30 atm.